UPDATED 08/19/11 3:11 p.m.

NAPERVILLE, Ill. (CBS)—  Some students at Naperville North High School are starting the school year with suspensions because they showed up for the first day of class after consuming alcohol, officials say.

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As CBS 2’s Vince Gerasole reports, at least 20 students were questioned by School District 203 officials. Now, 15, all seniors, have been suspended for 10 days each, and more suspensions may come.

Classes at the school began Wednesday. But school officials say students were drinking at three separate house parties before school began.

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Officials say an adult staff member encountered a student who appeared to have been drinking alcohol. Through a series of questions, it was determined a number of students had been drinking.

Principal Kevin Pobst said this is not simply teenage behavior that should be treated as young kids acting like teens typically do.

“We don’t laugh about teenage drug use or alcohol use,” Pobst said. “We see it as a safety issue. We want the students to get whatever attention they need, and it may not be very much attention, because they may be just experimenting. But it may be very serious attention that they need.”

The district is not reporting any of the students to police at this time, but the behavior may have violated several school rules.

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Beyond suspension, violating those rules could impact the ability of these students to take part in after-school activities and sporting programs.